A vehicle control device proposed in JP-11-51948 includes a CPU for calculating the vehicle wheel speed. The control device has an input capture function for capturing the time of an internal timer at which an edge is formed in a waveform of a vehicle wheel speed signal. The wheel speed signal is inputted from a vehicle wheel speed sensor via an input interface circuit. The CPU calculates a wheel speed based on the captured time.
An accuracy of the wheel speed calculation is critical for an antilock brake system, and the operation of the input capture function is required to be continuously monitored. However, the input capture function is monitored only when the vehicle is determined as parked, and therefore not monitored when the vehicle is running.
The input capture function of the microcomputer for control may be monitored by another microcomputer. In this case, the other microcomputer performs the same calculation and comparison between both results of the calculations. Then, it determines whether the operation of the input capture function of the microcomputer for control is normal. However, the device becomes expensive with this configuration, which has impact on competitiveness of the device in the market.